First recorded iPhone 5 that is defective? When you shake it side to side, it makes a thumping rattle sound. Almost like something is loose inside the unit. Possibly a loose battery problem? This unit is brand new, just opened out of the box. FYI: The 2nd replacement unit does not do this, so this does not appear to be normal (not a gyroscope).

***FIX UPDATE*** (Sept. 25, 2012): It's a loose battery! To FIX simply push down (put pressure) on the front-glass of the iPhone, with the palm of your hand. The battery will stick back down. The thumping sound will stop after that.